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B.3. DNSBL Style Example

Imagine that, in addition to the domain records listed above, there
are these:
$ORIGIN _spf.example.com. mary.mobile-users A
127.0.0.2 fred.mobile-users A 127.0.0.2
15.15.168.192.joel.remote-users A 127.0.0.2
16.15.168.192.joel.remote-users A 127.0.0.2

Say that your sender policy requires both that the IP address is
within a certain range and that the reverse DNS for the IP matches.
This can be done several ways, including the following:
example.com. SPF ( "v=spf1 "
"-include:ip4._spf.%{d} "
"-include:ptr._spf.%{d} "
"+all" )
ip4._spf.example.com. SPF "v=spf1 -ip4:192.0.2.0/24 +all"
ptr._spf.example.com. SPF "v=spf1 -ptr +all"